Project Summary Data consistently point to a ?quality chasm? between routine mental health services and evidence-based practices (EBPs). One approach to improving mental healthcare that holds great potential is measurement- based care (MBC), which is grounded in frequent and systematic use of assessment tools to regularly track the processes and outcomes of care. MBC has broad support as an EBP, particularly for adults. However, MBC implementation is complex and MBC is implemented with high quality in fewer than 20% of community mental health settings. Healthcare systems are in dire need of guidance on how to focus MBC to maximize benefit, and identification of essential MBC components has been named as a key priority for research. These efforts have been hampered by a lack of data on the mechanisms of MBC. This pilot study will use a mechanism- driven approach to compare two models of measurement-based care (MBC) in youth-serving community mental health settings: Multidimensional MBC, which includes measures of multiple domains that are patient- centered, treatment-driven, and symptom-focused, and Unidimensional MBC, which includes symptom measures only. Multidimensional MBC provides feedback on a broader array of process and progress outcomes that may be more relevant to clients and provide more actionable feedback to clinicians, and thus should have a stronger impact on target mechanisms and client outcomes. However, unidimensional MBC is lower burden for patients and providers, so might have more implementation success. The study will employ a Type 1 Effectiveness Implementation Hybrid design to assess the comparative effectiveness of these two approaches in three community mental health clinics serving a diverse client population while gathering data to inform future implementation. The first aim of the study is to conduct preliminary development activities to ensure fit between the two MBC approaches, the measurement of mechanisms, and the clinical context. To accomplish this aim, stakeholder focus groups and interviews will be used to gather perspectives on the two MBC approaches and the proposed research strategies, analyses of existing data will be used to develop algorithms to identify clients whose treatment is on-track (OT) or not-on-track (NOT) for positive treatment outcomes, and a small pre-pilot of study procedures will be conducted with 5 clinicians and 20 adolescent clients. The second aim of the study is to conduct a pilot randomized controlled trial comparing the two MBC approaches. The study will be conducted program-wide as standard care at the participating clinics (N = 900 youth treated by 22 clinicians), with a subset of 400 youth and their caregivers completing additional research measures. Simultaneously, data will be gathered to address the third study aim, which is to conduct a mixed- methods analysis of implementation factors related to multidimensional and unidimensional MBC. If successful, this study will support a future, fully-powered trial that will provide important data regarding MBC mechanisms of action, effective MBC strategies, and successful MBC implementation strategies.